Roughly translated into English, the post goes on to say that Mozilla and Facebook have reached an agreement to distribute a Facebook Phone in the latter half of 2013 and that the phone is based on Firefox OS.

It’s illustrated with a handset decked out in Facebook blue and white with a log in prompt on the screen in Polish and Facebook Inc. stamped on the back.

Apparently the “official presentation will take pace on 26 February at the Mobile World Congress”, by none other than Facebook CTO Bret Taylor…which would be odd, as he left earlier this year.

As a straight-faced prank, this is not a bad one. A note at the end of the blog post says something along the lines of “Scheduling this for Friday, don’t publish until we get green light from Press”. And if you browse the comments, a few attentive readers have left comments noting the specific day of publishing.